Reactive Oxygen Species (ROS) are diverse small signaling molecules which are highly reactive with unpaired valence electrons. ROS include superoxide (O2−), hydrogen peroxide (H2O2), hydroxyl radical (OH.), Nitric Oxide (NO) and peroxynitrite (ONOO−). Although ROS have some physiological functions, excessive generation may lead to imbalanced homeostasis of the biological system. ROS are constantly generated through a variety of pathways, including both enzyme-catalyzed and nonenzyme reactions.
Whenever the balance between ROS generation and the natural antioxidant defense system is distributed, a series of events may occur, deregulating cellular functions, which may lead to various pathological conditions for almost all vital organs. Activated immune cells like macrophages neutrophils and microglia start overexpressing several enzymes, including iNOS, NADPH oxidase, COX-2, and myeloperoxidase responsible for inflammatory processes mediated by oxidative stress. These enzymes contribute to the pathogenesis of various diseases. ROS-Generating multimeric enzymes are indispensable for protecting the host against infections and injuries. However, inappropriate activation of these enzymes may be harmful in noninfectious autoimmune disorders. Thus the discovery of various novel agents that can inhibit the activation of these enzymes may be therapeutically significant in ameliorating various diseases, including rheumatoid arthritis, atherosclerosis and neurodegenerative diseases.